If you are reading this on a tablet, it may well be one of a record number of devices shipped in the fourth quarter, 52.5 million, according to a preliminary estimate by IDC. That's a figure that surpassed predictions and illustrates how fast the lightweight but powerful portable computers are taking the world by storm.

Using its Worldwide Quarterly Tablet Tracker, IDC estimated that the market grew more than 73 percent over the same quarter of 2011, when 29.9 million tablets were sold.

And the numbers show that holiday shopping was a particularly strong shot in the arm for the market: Sequentially, sales rose 74 percent from just 30 million tablets shipped in the third quarter. The biggest growth in shipments came from Taiwanese manufacturer Asus,, which saw a 402 percent boost in shipments and more than doubled its market share from 2 percent to 5.8 percent.

Beating PCs

"We expected a very strong fourth quarter, and the market didn't disappoint," said Tom Mainelli, research director for tablets at IDC. "New product launches from the category's top vendors, as well as new entrant Microsoft, led to a surge in consumer interest and very robust shipments totals during the holiday season.

"The record-breaking quarter stands in stark contrast to the PC market, which saw shipments decline during the quarter for the first time in more than five years."

Apple, whose iPad broke open the marketplace when it was introduced in 2010, continues to dominate the market, but it's losing some ground, slipping from 51 percent in 2011's final quarter to 43.6 percent this time around. Apple increased its shipments, though, for the year, because of the introduction of the iPad mini and a full-size, fourth-generation iPad. (This month the Cupertino, Calif., technology giant also announced a new 128-GB iPad aimed at business users, further indicating it will try to match the diversity of its rivals' offerings.

Speaking of, Samsung's growth during 2012 by far outshined Apple, with a 263 percent increase over last year, now owning 15.1 percent of the global market with its Galaxy devices, more than double its 7.3 percent share last year. Amazon came in third place with its Kindle Fire tablets, but the online retail king lost market share, despite introducing a new device in September, slipping from 15.9 percent to 11.5 percent.

Also enjoying a spot in the top five was book giant Barnes & Noble, which sold 1 million Nook tablets and readers, although its market share sank from 4.6 percent to just 1.9 percent year over year.

A Milestone Reached

Charles King, principal analyst at Pund-IT, said the most interesting news here is that Apple's market share fell below 50 percent for the first time.

"That doesn't mean instantaneous doom and gloom for Apple -- the company is still the largest single tablet vendor around," King told us. "But it suggests that Android's growing dominance in smartphones is translating into the tablet market, as well. "

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